Microfluidic device for cell capture and isolation

ABSTRACT

Described herein are devices for capturing or isolating a biological cell from a sample, the device comprising a capture bed comprising a wave-herringbone surface pattern; and a plurality of nanostructures. Methods of making and using the same are also described.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 61/937,709, filed Feb. 10, 2014, entitled “Microfluidic Devices andMethods of Using Same”, the contents of which are hereby incorporatedherein in their entirety.

BACKGROUND

Non-invasive in nature, blood tests are the most commonly performedscreening and diagnostic tests to reveal a rich amount of information ofone's health state, ranging from chemistry and serology to hematologyand immunohematology. Recently, disease specific cells existing inextremely low concentration in blood have been identified as newdiagnostic and prognostic markers. For example, circulating tumor cells(CTCs) in peripheral blood are recognized as a critical cellular linkbetween the primary malignant tumor and the peripheral metastases ofpatients with lung, prostate, colon, breast, liver, and ovarian cancers.However, current technology platforms lack the ability to reliablyseparate and detect rare cells in an extremely low quantity, down to1-10 cells per billion red blood cells. As a result, there is no “goldstandard” rare-event analysis method for measuring rare cells such asCTCs.

Conventional cell separation techniques including density gradientcentrifugation, preferential lysis of red blood cells, ficoll-hypaquedensity centrifugation, porous filters and immunoaffinitychromatography, rely on size, density, rigidity and specific surfaceantigens to isolate desired cell subpopulations. These methods usuallyrequire laborious manual and bulk sample preparation steps, resulting inhighly variable results and low sensitivity. The more recent molecularmethods such as PCR-based detection, suffer from loss of live cells forother analysis.

Several rare-event imaging systems, including the rare event imagingsystem (REIS), fiber optic array scanning technology (FAST), andautomated digital microscopy, have been developed to store images forre-examination without actual cell recovery. However, the number ofcells to be evaluated to find rare cells is prohibitively large and theimaging modalities are rather cumbersome and complicated.

In comparison, lab-on-a-chip microfluidic devices have becomeincreasingly attractive for blood analysis as they allow for gentlemanipulation and precise control of microenvironment of individual cellsin blood. However, none of the existing lab-on-a-chip approaches basedon cell physical properties have offered reliable and rapid isolation ofCTCs from the whole blood with minimal sample preparation.

Immunoaffinity cell isolation uses antibodies recognizing CTC specificsurface antigens to achieve high specificity. However, the sensitivityof CTC detection is low and highly variable for clinical applications.

Although progress in the technology space has been made, in order toexplore the benefits of CTCs in metastatic cancer, there is a need todevelop cell sorting technologies that specifically target rare CTCswhile meeting the sensitivity, purity, high throughput, live cell andautomation requirements. Embodiments of the present invention aredirected to meeting these needs.

SUMMARY

Some embodiments of the present invention provide a microfluidic devicecomprising a 3D hierarchically structured substrate—specifically, amicroscale rippled surface decorated with nanopillar array ornanoparticles to accommodate the multi-scale characteristic dimensionsof cancer cells and optimize cell capture in a microfluidic platform.

In some embodiments, embodiments of the present invention comprise asubstrate comprising hierarchical surfaces that mimic natural surfaces;and therefore, maximize efficiency. For example, the small-intestine hasa folded/rippled surface (plicae circularizes), villi, and microvilli,which increase the absorptive surface area by several folds. Many cells,including cancer cells, are also found to contain membrane extrusions onthe order of 100 nm for effective interactions with the environment.

In some embodiments, embodiments of the present invention comprisemulti-scale structures to match both the cell dimension and membraneextrusions, respectively.

In some embodiments, the microscale surface in the form of ripples orherringbones aims to create hydrodynamic force to improve cell-surfacecollision frequency. When blood flows in a microchannel under a laminarflow, the large number of red blood cells easily shields the rare CTCsfrom the antibody coated substrate. In addition, the low shear regionnear any surface in the flow stream creates a thin lubrication layer tolimit the number of contacts between the cells and the antibody-coatedsurfaces. A microstructured substrate is expected to improve thecollision between the cell and antibody-coated walls through microvortexor centrifugal flow patterns.

It is believed that micro-/nanostructured surfaces, including nanoposts,nanowires and nanoparticles, not only increase surface area, but alsoenhance local topographic interactions with cell membrane structuressuch as microvilli and filopodia, which in turn benefits both captureefficiency and specificity.

Some embodiments of the present invention provide herringbone structureswith smoothly curved undulations through created through surfacebuckling, which will eliminate the low shear sharp corners prone tonon-specific binding. The smoothly curved undulation is also expected toreduce high shear regions in the sharp-corner devices, causing lessdamage to the cells. Alternatively, parallel micro-ripples may befabricated to induce centrifugal forces to encourage cell/substratecollision.

In some embodiments, the engineered nano-structures will match the sizeand density of microvilli on a tumor cell membrane, which have anaverage radius of 50 nm, length of 2 μm, and density of 13 per 100 μm².Since the microvilli on leukocytes are thicker in diameter compared tocancer cells by a couple of hundred nanometers, embodiments of thepresent invention are designed to have improved size complementaritybetween the capture bed and cancer microvilli, which is expected toenhance cell-surface adhesion strength and encourage specific tumor cellcapture. In some embodiments, the flexibility of the nanostructures ismodified by creating them in different soft materials with Young'smoduli ranging from MPa to KPa to reduce potential cell damage. In someembodiments, the combination of nanostructure and soft materials willallow for enhanced local topographic interactions with the nanoscalecomponents of the cellular surface (e.g., microvilli and filopodia),leading to vastly improved cell-capture affinity compared tounstructured surfaces or surfaces with a single scale feature.

Some embodiments provide multiscale topographies: e.g., microscale forhydrodynamic effect and nanoscale for nanostructure interactions topromote isolation of rare cells in an immunoaffinity microfluidic chip.

In some embodiments, the surface has three distinct features. In someembodiments, these features enhance both rare cell capture efficiency(number of captured cells/total number of target cells) and selectivity(captured target cells/total number of captured cells). Some embodimentsprovide:

1) a microscopic wavy surface (1D ripples or 2D herringbones) will befabricated to enhance cell margination and binding. The pattern,wavelength, and amplitude may be fine-tuned to enable larger surfacecontact area for cell and optimal hydrodynamic efficiency. In someembodiments, due to the non-uniform shear stress distribution, themajority of captured cells will be located in the troughs of theperiodic waves, allowing for accurate cell counting;

2) nanopillar arrays or nanoparticles that match the nanostructures onthe cell surface (e.g. microvilli or filopodia) designed and integratedwith the above fabricated microscopic wavy patterns to enhance cell-wallinteraction and adhesion strength;

3) controlled flow shear rate in a microfluidic channel to allowspecific cell capture; and

4) minimized non-specific binding as a result of the smoothly curvedmicrostructures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a prior art surface pattern.

FIG. 2 depicts an exemplary capture bed of the present invention havinga wave-herringbone surface pattern.

FIG. 3 depicts a schematic of an exemplary microfluidic device of thepresent invention.

FIG. 4 depicts a side view zoom of an exemplary hierarchical surfacepattern of the present invention.

FIG. 5 depicts an exemplary hierarchical surface pattern of the presentinvention having nanopillars.

FIG. 6 depicts a side view zoom of cell trapping in an exemplary surfacepattern of the present invention.

DETAILED DESCRIPTION

The present inventors have developed a computational model for studyingtransport and adhesion dynamics of particles and cells, e.g.,arbitrarily-shaped objects under fluid flow. As the present inventorshave discovered, cell capture rates are largely influenced by surfacemorphology.

In some embodiments, the present invention provides methods of capturinga cell or a particle from a biological sample. In some embodiments, themethod comprises the step of flushing the capture bed after it iscontacted with a sample, to measure the adhesion strength of a capturedcell. In some embodiments, the method demonstrates the higher adhesionstrength provided by a larger curved contact area.

In some embodiments, shear rate is used to control the selectivity ofthe capture process. In some embodiments, the methods of the presentinvention take advantage of the fact that tumor cells have overexpressed biomarkers on their membranes. Some embodiments of the presentinvention provide methods that separate tumor cells from white bloodcells (WBCs). For example, the expression levels of the epidermal growthfactor receptor (EGFR) or epithelial cell adhesion molecule (EpCAM) incancer cells can be ˜100 times higher than those in normal cells. Withhigher adhesion receptor density on the membrane, CTC cells require alarger shear force to detach from surfaces coated with correspondingantibodies. By controlling the shear rate within a certain range, CTCmight be able to adhere to the surface while WBC will be washed away.The computational results agree well with the experimentally data withprimary human glioblastoma (hGBM) cells (a surrogate for CTCs).

In some embodiments, the shear rate required to separate CTCs from WBCsis from about 20 s⁻¹ to about 200 s⁻¹. In some embodiments, the shearrate required to separate CTCs from WBCs is from about 20 s⁻¹ to about175 s⁻¹. In some embodiments, the shear rate required to separate CTCsfrom WBCs is from about 20 s⁻¹ to about 150 s⁻¹. In some embodiments,the shear rate required to separate CTCs from WBCs is from about 20 s⁻¹to about 125 s⁻¹. In some embodiments, the shear rate required toseparate CTCs from WBCs is from about 20 s⁻¹ to about 100 s⁻¹. In someembodiments, the shear rate required to separate CTCs from WBCs is fromabout 20 s⁻¹ to about 80 s⁻¹. In some embodiments, the shear raterequired to separate CTCs from WBCs is from about 20 s⁻¹ to about 60s⁻¹. In some embodiments, the shear rate required to separate CTCs fromWBCs is from about 20 s⁻¹ to about 40 s⁻¹.

In some embodiments, the device is configured to generate microvorticesinside the capture bed to increase cell-wall collision frequency andavoid a flow recirculation vortex near the capture wall surface, whichcould potentially lead to non-specific trapping of cells. For example,the cross-sectional view depicted in FIG. 6, shows chaotic microvorticesthat help cells mix and collide with the wall. FIG. 4 provides a sideview having a smooth shear flow near the rippled surface, which will nottrap cells like traditional rectangular microgrooves. In someembodiments, a Dean Number of 35.9 is the threshold value for the onsetof flow instability. Dean number is calculated using the followingequation:De=(pvD/μ)(D/2R)^(1/2)

-   -   wherein R is the radius of curvature; and    -   D is the hydraulic diameter of the channel.

Another advantage of the inventive design is the minimization of areaswith high shear forces that may damage the cells. The actual flowpatterns for complex geometries such as the inventive wave-herringbonesurface pattern may be created and optimized using computational fluiddynamics simulation. In some embodiments, wavelength and channel heightare optimized to maximize cell-wall collision and increase captureefficiency.

In some embodiments, the micro-structured surface pattern comprises aPDMS/oxide bilayer. In some embodiments, the micro-structured surface isprepared by buckling of the PDMS/oxide bilayer, wherein the pattern andwavelength of the wavy surface is determined through computationalmodeling. In some embodiments, a wave-herringbone surface pattern isthen replicated on stress-free films, e.g. PDMS. PDMS is selected heredue to its biocompatibility, low modulus, and wide knowledge of itsapplications in microfluidics.

In buckling, the wavelength (λ) and amplitude (A) of the wrinkles can betuned by varying the elastic modulus of the PDMS substrate and thethickness of the top silicate layer, which are controlled by the mixingratio of the PDMS resin/crosslinker, UVO/O2 exposure time, the modulusand thickness of the hard layer, and the applied strain.

In general, the aspect ratio of the surface patterns of the presentinvention are ≤0.3(A/λ). In some embodiments, wrinkles can evolve from1D ripples into various 2D patterns, including bifurcated wrinkles,labyrinths, and herringbones, depending on the anisotropy of the appliedforces and stress release sequence, which will guide the energy releasepath. In some embodiments, the wrinkle size and shape are fine-tuned toproduce wave-herringbone patterns that generate efficient microvorticesfor cell-wall collision while reducing non-specific cell trapping.

In some embodiments, the fabricated PDMS pattern is directly used in thecapture bed of the microfluidic devices of the present invention. Insome embodiments, the PDMS surface is functionalized with specificcapturing agents, e.g. antibodies. In other embodiments, the PDMSpatterns can be used as molds to replicate on different substrates withvery different Young's moduli, including epoxy, hydrogels (e.g.poly(2-hydroxyl ethyl methacrylate, PHEMA, and polyacrylamide), PMMA,and poly(styrene) (PS) using established soft lithography techniques,such as replica molding, nanoimprint and capillary force lithography.

In some embodiments, the antibody will be coated on these materialsthrough standard chemistry to functionalize a hydroxyl group, carboxylgroup (directly or from hydrolyzed ester group), amine group, or simplythough physisorption.

In some embodiments, to create pillar arrays on a microripple surface, aPDMS pillar array is fabricated, which will then be stretched, followedby O₂ plasma or UVO treatment. In some embodiments, after release ofstrain, microripples are formed with built-in pillars. The wavelengthand amplitude of the microripples may be determined by stretching strainlevel, plasma or UVO treatment time and power, as well as the Young'smodulus of the PDMS film—similar to wrinkle formation on bulk PDMS film.

In some embodiments, the tilt angle of the pillars is determined by thestretching angle between stretching direction, x, and pillar latticeaxis, k. In some embodiments, the degree of pillar tilting on wrinklesis highly dependent on PDMS film thickness.

In some embodiments, after stretching and oxygen plasma treatment, thePDMS bilayer film is dip-coated with silica nanoparticles to introducenano-scale roughness, which can be subsequently functionalized withsilane and a specific antibody. After releasing the initial strain, thedual-structured surface is obtained. Alternatively, a microcontactprinting technique to pick up the nanoparticles using a stretched PDMSwrinkled surface can be used.

In both hierarchical structures, the wavelength/amplitude of themicroripples, the wave-herringbone surface pattern, the size ofnanoparticles, pillar diameter, spacing, and aspect ratio are designedto match microvilli structure. The density of the nanostructure coverageon the surface pattern is also designed in view of these structures.

In addition, soft and stable PDMS materials with Young's moduli as lowas ˜250 KPa can be prepared, which are compatible with the fragilenature of CTCs. In addition, the desired surface patterns can bereplicated to lower modulus materials, such as poly(ethylene glycolmethacrylate) (PEGMA) and polyacrylamide (PA).

A typical integrated microfluidic testing device is illustrated in FIG.3. The fabricated hierarchical surface may be covered with a PDMStransparent top with two parallel channels or a single channelencapsulating a half flat and half rippled surface via PDMS-PDMS or O₂plasma bonding. Some embodiments provide a transparent device thatallows in-situ observation of the cell capture by fluorescencemicroscopy.

In some embodiments, the channel height may vary from about 20 μm toabout 60 μm. In some embodiments, cells or microparticles will be driventhrough the microchannels by a programmable syringe pump. The images canbe captured by a cooled CCD camera.

Flat covers, rippled complimentary covers, and rippled non-complimentarycovers may all be viable options. To create two self-aligned PDMS ripplesurfaces, PDMS can be cast on a PDMS rippled surface. After curing, therippled interface can be separated by inserting a thin glass cover slipor wire between the two rippled surface and monitored under an invertedoptical microscope. In such an embodiment, the two PDMS strips will beself-aligned, each having complementary ripples on their surface.

In some embodiments, the devices of the present invention providemultiscale cell adhesion dynamics that model cell transport in flow andinteraction between the wrinkled surfaces while keeping ligand-receptorbinding details. Some embodiments provide a hierarchical wrinkle surfacehaving dual size matching: microscale sinusoidal ripples with tunablewavelength to match the cell size, and nanopillars with tunablesize/density to be complimentary with that of microvilli on the cellsurface. Without being bound by theory, it is believed that the uniquedual-size matching significantly and selectively enhances the captureand adhesion of cells of a particular size and surface property, andavoids non-specific trapping or possible cell damage.

In some embodiments, the present invention provides a patterneddistribution of captured cells throughout separated troughs, whichallows fast/automatic cell counting. An additional advantage provided bythe devices of the present invention is that the hierarchical structurecan be mass produced, making it attractive for potential integration inglobal health care devices.

In some embodiments, the devices of the present invention comprise awavy micropatterned microfluidic device for capturing circulating tumorcells from whole blood with high efficiency, selectivity and throughput.

In some embodiments, a capturing agent is immobilized on the substrate.In some embodiments, a capturing agent is immobilized on the substratewhich selectively captures circulating tumor cells while not interactingwith other cells present in the whole blood.

In some embodiments, the substrate surface has repetitivewave-herringbone structures. In some embodiments, the substrate surfacehas repetitive wave-herringbone structures, which can induce arotational flow. In some embodiments, the rotational flow can enhancethe collision of circulating tumor cells with the substrate surface,therefore increasing the capture efficiency of the circulating tumorcells.

In some embodiments, the wave-herringbone surface pattern (topography ofthe substrate surface) differs from a traditional herringbone groovestructure in the fact that it is comprised of sinusoidal waves extendingin two directions as opposed to sharp ridges. This structure can alsokeep the morphology of circulating tumor cells intact, which isimportant for various post-analyses.

In some embodiments, the proposed microfluidic device is comprised of asubstrate surface and a cover, which are combined to form a flowchannel. Some embodiments provide an inlet reservoir and an outletreservoir. In some embodiments, the inlet reservoir and/or the outletreservoir are punched in the device.

In some embodiments, a sample is injected through the inlet reservoir,passing through the flow channel and then reaching the outlet reservoir.In some embodiments, the sample is a biological sample. In someembodiments, the biological sample is whole blood.

In some embodiments, the rotational flow induced by the repetitivewave-herringbone structures can enhance the capture efficiency ofcirculating tumor cells while all other cells flow through in astreamlined fashion reaching the outlet reservoir.

In some embodiments, the applied shear rate to the device can range from10 s⁻¹ to 2000 s⁻¹. In some embodiments, the applied shear rate to thedevice can range from 30 s⁻¹ to 500 s⁻¹.

In some embodiments, the wave-herringbone surface pattern has acharacteristic angle ranging from about 30 degrees to about 120 degrees.In some embodiments, the lateral length of this structure can range fromabout 100 μm to about 1000 μm, and the longitudinal length is calculatedaccording to the characteristic angle.

In some embodiments, the wave-herringbone surface pattern can havevalues ranging from 40 μm to 100 μm in terms of wavelength and 13 μm to33 μm in terms of amplitude. In some embodiments, the depth of the flowchannel is from about 40 μm to about 100 μm, and the overall size of theflow channel is from about 200 μm to about 4000 μm in terms of width andabout 0.5 cm to about 1.5 cm in terms of length.

Some embodiments of the present invention provide a capture efficiencyof greater than 80%, with high purity. Some embodiments of the presentinvention provide a capture efficiency of greater than 85%, with highpurity. While other embodiments provide a capture efficiency of up to90%, with high purity. Some embodiments of the present invention providea capture efficiency of greater than 95%, with high purity. Someembodiments of the present invention provide a capture efficiency ofgreater than 96%, with high purity. Some embodiments of the presentinvention provide a capture efficiency of greater than 97%, with highpurity. Some embodiments of the present invention provide a captureefficiency of greater than 98%, with high purity. Some embodiments ofthe present invention provide a capture efficiency of greater than 99%,with high purity.

As shown in FIG. 3, some embodiments of the present invention provide adevice comprising an inlet and an outlet. In some embodiments, twopieces of tubing serve as the inlet and the outlet. In some embodiments,the sample is injected through the inlet and passes to the outlet. Insome embodiments, the bottom layer of the channel is comprised of aplurality of smooth curves, with the left section depicting these smoothcurves; and the blue spheres represent circulating tumor cells.

In some embodiments, the device achieves higher capture efficiency whencompared with other methods, due to the enhanced rotational flow inducedby the wave-herringbone surface pattern.

In other embodiments, the device allows for easy fabrication without theneed for a cleanroom, which is in contrast to traditional fabricationprocesses which need soft-photolithography to make the mold in thecleanroom.

In some embodiments, the devices can achieve a higher throughput, due tothe large cross-area in the device. This advantage can reduce the timefor the blood test, thus significantly increasing the efficiency.

In some embodiments, the device has the ability to capture circulatingtumor cells while maintaining the cells' natural morphology, due to thesmooth sinusoidal curve patterning.

In some embodiments, the device comprises smooth sinusoidal wavepatterns which force cells to roll over the curve and reach the trough.Thus, cell imaging after the flow test simply requiresclinicians/researchers to scan the trough regions to gain theinformation of the captured circulating tumor cells.

In some embodiments, the device is used for the high efficiency captureof other biological cells or analytes after the immobilization ofcorresponding capturing agents.

In some embodiments, the lateral dimension of the wave-herringbonestructure can be decreased to the order of 1 μm and increased to theorder of 1 mm. In some embodiments, the wavelength can be decreased tothe order of 10 μm and increased to the order of 200 μm. In someembodiments, the amplitude can then be accordingly decreased to theorder of 3 μm and increased to the order of 60 μm. In some embodiments,the depth of channel can be decreased to the order of 20 μm andincreased to the order of 200 μm. In still further embodiments, theoverall size of the flow channel can also be decreased to the order of10 μm and increased to the order of 1 mm.

In some embodiments, the devices comprise micro-scale sinusoidal ripplesand herringbone structures. In some embodiments, the devices comprisemicro-scale sinusoidal ripples and herringbone structures that generatemicro-vortices to enhance cell-wall collision, provide larger adhesionarea, avoid non-specific cell adhesion and possible cell damage, and/orenable accurate cell counting. In some embodiments, these nanostructureswill complement microvilli on cell membranes; and thus, improve bothinteraction specificity and cell capturing efficiency.

In some embodiments, cell imaging techniques are incorporated in theproposed device to detect the signals of cell capture.

In some embodiments, devices of the present invention are used byphysicians or clinicians to capture circulating tumor cells in apatient's whole blood, which then allows for various post-analyses to becarried out on intact cells. For example, with certain techniques,devices of the present invention could indicate the number of capturedcirculating tumor cells, which could serve as an indicator for specificdiseases. In other embodiments, after circulating tumor cells arecaptured, the cells could be analyzed to reveal their genetic andprotein information, thus providing a guide for potential treatments,and even the possibility of personalized treatment.

In some embodiments, the wave-herringbone surface pattern forms thesurface of the microfluidic channel. In some embodiments, the channelitself is a hollow channel while the pattern shows on the surface.

Referring now to the Figures, FIG. 1 depicts a surface pattern employedby conventional devices used to separate particles from a fluid. Asshown in FIG. 1, the surface patterns used to separate particles inconventional devices have an apex 110 with a sharp corner, which reducescapture efficiency and can damage cells.

In contrast, the surface patterns of the present invention, for exampleas depicted in FIG. 2, provide a smoother apex 220, which increases thecapture efficiency and avoids damage to the cells. FIG. 2 also depictsheight (h) spanning between apex 220 and the base of the surface pattern210. Height (h) is an important feature as the amplitude vs. wavelengthratio of the surface pattern has been designed for optimal captureefficiency. In some embodiments, the ratio of amplitude to wavelength isfrom about 1:2 to about 1:4. In some embodiments, the ratio of amplitudeto wavelength is about 1:3. In some embodiments, the distance (d) fromapex 220 to apex 220 is from about 30 microns to about 60 microns. Insome embodiments, distance (d) is from about 35 microns to about 55microns. In some embodiments, distance (d) is from about 40 microns toabout 50 microns. In some embodiments, distance (d) is about 45 microns.In some embodiments, distance (d) is about 50 microns.

FIG. 3 provides a plan view of an exemplary microfluidic device 300 ofthe present invention. As shown, in FIG. 3, some embodiments of thepresent invention include an inlet 310 and an outlet 320. The diametersof the inlet 310 and outlet 320 apertures can vary. A fluid flow acrossthe capture bed 330 of from about 358 ul/hr to about 5800 ul/hr istypically applied

In addition, FIG. 3 depicts the location of the hierarchical surfacepattern in the capture bed 330 of an exemplary microfluidic device 300.

The side view zoom depicted in FIG. 4, is an exploded view of thesection identified as “IV” in FIG. 3. As FIG. 4 demonstrates, surfacepatterns of the present invention have a much smoother surface thanconventional particle separation devices.

FIG. 5 provides an exploded view of the section identified as “V” inFIG. 4. As shown in FIG. 5, the hierarchical surface patterns of thepresent invention include nanostructures 510. FIG. 5 specificallydepicts these nanostructures in the form of nanopillars. However,nanostructures 510 can also take the form of nanospheres or protrusionsof almost any shape and dimension, as long as it provides the requisitecomplementarity to the surface structure of the cell being captured fromthe sample, e.g. the microvilli of a circulating tumor cell.

In some embodiments, the nanostructures have a height of about 1 micron,a diameter of about 100 nm. In some embodiments, the nanostructures arespaced at about 200 nm apart on the surface pattern. In someembodiments, the nanostructure diameter ranges from about 120 nm toabout 1100 nm. In some embodiments, the nanostructures are spaced at adistance of from about 50 nm to about 800 nm from each other.Nanostructure spacing has been found to directly impact the captureefficiency and specificity.

FIG. 6 depicts an exploded view of the section identified as “VI” inFIG. 3. Specifically, FIG. 6 depicts the capture of circulating tumorcells 610, using an exemplary hierarchical surface pattern of thepresent invention 600. As shown in FIG. 6, the circulating tumor cells610 have microvilli 611. These microvilli 611 protrude from the surfaceof the circulating tumor cell 610. FIG. 6 also depicts red blood cells620 (RBC) which are selectively separated from the circulating tumorcells 610 by the hierarchical surface pattern of the present invention600.

The invention will be described in greater detail by way of specificexamples. The following examples are offered for illustrative purposesand are not intended to limit the invention in any manner. Those skilledin the art will readily recognize a variety of noncritical parameters,which can be changed or modified to yield essentially the same results.

EXAMPLES Example 1

Preliminary studies have been carried out by injecting 2 μm fluorescentparticles into a PDMS microchannel consisting of half rippled (20 μmwavelength) and half flat surface under flow shear rates of 30⁻¹ and 90s⁻¹ to study the particle distribution. The individual particles andtheir movement are monitored in situ. Very few binding events occurredon the flat surface. In contrast, many microparticles were clearly boundon the rippled surface, most of which were located on the same plane asthe troughs of the ripples, which is favorable for cell counting.

Example 2

Four cells are released at the inlet of a 40 μm high channel under ashear rate of 20 s-1 and periodic boundary conditions are applied at theinlet and outlet. After three seconds, two cells are captured on therippled surface while no cells are captured on the flat surface. Thenumber of cells captured on a rippled surface is found to be much largerthan that on a flat surface, which demonstrates that the rippled surfacehelps cell margination and contact with the wall surface. The cell-wallinteraction is accurately modeled with ligand-receptor binding/breakingdetails. Besides increased capture rate, the adhesion strength of therippled surface is also predicted to be much higher than that of theflat surface.

Example 3

An exemplary device of the present invention is tested with lung cancerepithelial cell NCI-H1650 and the prostate cancer cell PC3, which havebeen widely used as model cell lines for optimizing CTC diagnostics. Theinterior surfaces of the test device is functionalized though silanechemistry and biotinylated antibody, followed by blocking with albumin.For substrates other than PMMA, specific antibodies are coated onto themthrough standard chemistry to functionalize the hydroxyl group, carboxylgroup (directly or from hydrolyzed ester group), amine group, or simplyphysisorption. Cell suspensions containing 10-10000 cells/mL in bufferor spiked in healthy donor's blood are flowed through the microchips atthe optimal flow shear rate range as determined by computational andmicroparticle capture studies. The cell concentration range is designedto cover the CTC concentration in cancer patients of different stages.The captured cells are stained by anti-CD45 (a leukocyte marker),anti-cytokeratin (a specific marker for tumor cells originated fromepithelial), and DAPI (nucleus stain). The number of captured H1650/PC3cells and leukocytes are counted under an optical microscope todetermine the capture efficiency and purity. The location of capturedcells on the hierarchical surfaces is also documented. The captureyields on flat, micro-feature only, nano-feature only and hierarchicalsurfaces are compared.

TABLE 1 Surface Pattern Capture Efficiency (%) Flat 6.2 Wave 26.8Herringbone 76.5 SP 1 86.7

The results described in Table 1 (above) demonstrate that an exemplarydevice of the present invention, having a rippled herringbone (orwave-herringbone) surface pattern (SP 1), has the highest captureefficiency—around 90%. These results demonstrate the unexpectedimprovement in capture efficiency provided by an exemplary surfacepattern of the present invention.

It is intended that any patents, patent applications or printedpublications, including books, mentioned in this patent document behereby incorporated by reference in their entirety.

As those skilled in the art will appreciate, numerous changes andmodifications may be made to the embodiments described herein, withoutdeparting from the spirit of the invention. It is intended that all suchvariations fall within the scope of the invention.

The invention claimed is:
 1. A device for capturing a biological cellfrom a sample, the device comprising: a capture bed comprising: awave-herringbone surface pattern having a ratio ofamplitude-to-wavelength that is 1:2; and a plurality of nanostructures;wherein the wave-herringbone pattern and the plurality of nanostructuresare integrated on a single surface; and wherein the nanostructures areequidistantly spaced in the capture bed.
 2. The device according toclaim 1, wherein the nanostructures are selected from the groupconsisting of nanopillars; nanospheres; and a combination thereof. 3.The device according to claim 1, wherein the nanostructures each have anaverage diameter of from 100 nm to 1500 nm.
 4. The device according toclaim 1, wherein the equidistant spacing between nanostructures beselected from a distance ranging from 100 nm to 250 nm.
 5. The deviceaccording to claim 1, wherein the wave-herringbone surface patterncomprises sinusoidal-like waves extending in two directions.
 6. Thedevice according to claim 1, wherein the wave-herringbone surfacepattern is configured to form channels in the capture bed.
 7. The deviceaccording to claim 6, wherein the channels have a height of from 20 μmto 100 μm.
 8. The device according to claim 1, further comprising: aninlet; and an outlet; wherein the outlet is positioned at a distancefrom the inlet; and wherein the sample flows from the inlet to theoutlet.
 9. The device according to claim 8, wherein the sample flowsfrom the inlet to the outlet at a rate sufficient to capture abiological cell from the sample.
 10. The device according to claim 1,wherein the capture bed further comprises a capturing agent.
 11. Thedevice according to claim 10, wherein the capturing agent is selectedfrom the group consisting of: an antibody; and an aptamer.
 12. A kit forisolating a target cell from a sample comprising the device according toclaim 1; and instructions for using said device.